1. Field of the Invention
The present invention relates to a vehicle lamp unit such as a stop lamp, and, more particularly, to a vehicle lamp unit that uses a light emitting diode (LED) having a high directivity as a light source.
2. Description of the Related Art
The vehicle lamp unit using LEDs as a light source is getting popular recently. However, because an ordinary LED has a high directivity, a light emission range of one LED is extremely narrow. Consequently, the vehicle lamp unit requires a number of LEDs to satisfy light distribution specifications such as an amount of light (intensity and luminance), which increases manufacturing costs of the vehicle lamp unit.
Some vehicle lamp units are developed to satisfy the light distribution specifications with less number of LEDs by widening the light emission range of the LED. This type of vehicle lamp unit is disclosed, for example, in Japanese Patent Application Laid-Open No. 2000-276905 and Japanese Patent Application Laid-Open No. 2002-270009. FIGS. 1A to 1C are schematics for explaining a conventional vehicle lamp unit. The conventional vehicle lamp unit has an LED 100 having a high directivity as a light source and a reflective surface 101 that reflects light beams L3 emitted from the LED 100 in a predetermined direction.
When the LED 100 emits a light, the light beams L3 from the LED 100 are reflected by the reflective surface 101 in a predetermined direction. Light beams L4 reflected at the reflective surface 101 are radiated to the outside with a predetermined light distribution pattern. The conventional vehicle lamp unit is configured to satisfy the light distribution specifications with less number of LEDs 100 by using the reflective surface 101.
The shape of the reflective surface 101 based on a single paraboloid of revolution to satisfy a light distribution with less number of LEDs 100. In order to clear conditions on the amount of light to satisfy the light distribution specifications and conditions on less number of light sources (LEDs 100), the conventional vehicle lamp unit is required to make effective use of the light beams L3 emitted from the light sources (LEDs 100). Therefore, by using the reflective surface 101, the conventional vehicle lamp unit effectively uses the light beams L4 obtained by reflecting the light beams L3 from the light sources (LEDs 100) at the reflective surface 101.
However, if the LED 100 having a high directivity is used as the light source, an F value (focal length) of the paraboloid of revolution for the reflective surface 101 becomes smaller than usual. Therefore, with the conventional vehicle lamp unit, a range of the light beams L4 reflected from the reflective surface 101, i.e., a light emission range of the reflective surface 101, is limited to some extent, and therefore, it is not possible to expand the light emission range.
Outside dimensions A and B of the reflective surface 101 based on the single paraboloid of revolution when viewed from a front side are restricted by a depth C of the reflective surface 101. In other words, there is a correlation between opening dimensions A and B of the paraboloid of revolution and the depth C. Then, the depth C of the reflective surface 101 is restricted by the F value of the paraboloid of revolution for the reflective surface 101.
For example, when aluminum is evaporated onto the reflective surface 101, there is a correlation between the depth C of the reflective surface 101 onto which aluminum can be evaporated and the F value of the paraboloid of revolution for the reflective surface 101. The F value thereof becomes small when the LED 100 having a high directivity is used as the light source. As a result, restriction of the F value causes the depth C of the reflective surface 101 to be small.
Furthermore, the outside dimensions A and B of the light emission range of the reflective surface 101 are restricted to be small by the restriction of the depth C to be small. The light emission range of the reflective surface 101 of FIG. 1A to FIG. 1C is a circle inscribed in a rectangle i.e. an almost square (A=B) of an outside dimension width A and an outside dimension length B.
In addition, the shape of the light emission range of the reflective surface 101 is an almost circle. If the light emission range of the reflective surface 101 is a rectangle or an almost square inscribed in the circle, it is necessary to form a straight wall D in the reflective surface 101 by cutting the paraboloid of revolution for the reflective surface 101, as shown in FIG. 1C. In this case, dimension E of the rectangular light emission range becomes smaller than the dimensions A and B of the light emission range that is the almost circle circumscribing the rectangle. As explained above, the conventional vehicle lamp unit has the problems such that the light emission range of the reflective surface 101 is limited to some extent, which causes the light emission range not to be widened.